Ashok Mehta, an employee in Delhi’s Transport Department, had plans to travel to the desert state of Rajasthan on Thursday Nov. 14, the start of his niece’s wedding celebrations and, until this week, a public holiday in India.

The 53-year-old, his wife and daughter, had booked travel tickets and were excited to attend the first day of the four-day wedding when they would give their niece a set of red and cream ivory bangles, known as the “chudha,” a signature accessory for Indian brides.

But on Monday their plans were undone when government employees were informed that their holiday, marking the Islamic holy day of Ashura, had been shunted back a day: Because of the moon.

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The date of Ashura, the Islamic remembrance for the martyrdom of Hussein ibn Ali, the grandson of the Prophet Muhammad, is determined by the moon. The holiday falls on the tenth day of the first month of the Islamic lunar calendar, also known as Muharram. Months in the Muslim calendar vary in length between 29 and 30 days, depending on when the new moon appears.

This year, astrological charts had predicted that Ashura would fall on Nov. 14, but some Muslims shun the charts, preferring to spot the moon with the naked eye before declaring the start of a new month. Special moon-sighting committees are dedicated to making that call.

When Delhi’s main moon-sighting committee met to spot the new moon at the Jama Masjid, one of India’s largest mosques, on the evening of Nov. 4 and were not able to see it, they declared that the first day of Muharram would be Nov. 6, a day later than predicted. Ashura was delayed by a day. So too were the plans of Mr. Mehta and hundreds of thousands of government employees like him because the Delhi government goes by the sighting of the moon by the Jama Masjid committee. Mr. Mehta said he was now “duty bound” and along with his family, will have to skip the first day of revelry. “I couldn’t have taken the day off at such a short notice,” he added.

To deal with the unpredictable nature of the moon, which determines when festivals including Eid and Ramadan should be observed, the Indian government has a contingency plan.

A government directive issued in June 2012, states that information about changes to the date of these festivals affecting workers will be communicated in a formal order.

In case of short notice, the offices of the central government must listen out for announcements made by India’s state run broadcaster, Doordarshan or radio station, All India Radio. The message can be passed on via newspapers too, the order said. This year is the first time for many years when a change has been required.

“Yes, this has happened after a long time,” Ashok Kumar, the signatory of the Nov. 11 notice issued by the Department of Personnel and Training, part of the Ministry of Personnel, Public Grievances and Pensions, which amongst other responsibilities, oversees any information relating to public holidays.

“But these things happen and no one has any control over it,” added Mr. Kumar who is a deputy secretary in the department.

On Thursday, India’s National Stock Exchange and the Bombay Stock Exchange also followed suit and announced Nov. 15 as the revised date for the holiday.

The markets will have a shorter time than usual to react to wholesale price inflation data, published by the government Thursday, before the holiday Friday.

According to reports, the announcement also affected students at the University of Mumbai, as examinations scheduled for Nov. 15 have been postponed.

Countries marking Ashura that take their lead on moon sightings from Saudi Arabia, will however, observe the holiday on Nov. 14, as the Saudi Supreme Court pronounced that the sacred month of Muharram began on Nov. 5.

The Saudi Supreme Court normally bases its decisions on moon sightings by official astronomical committees.

In the past, the Fiqh Council of North America, a group of Islamic scholars who endorse scientific calculations over physical moon sightings, has opined that computing these dates astronomically, is the only accurate determinate of the lunar months. They argue that using scientific data allows devotees across the world to be united in celebrations, or in the case of Ashura, mourning.

So confusion ensues, not just at this time of year, but even on several Hindu festivals like Diwali and Guru Nanak Jayanti, the dates for which vary each year depending on the sighting of the moon. Some Indians think that keeping pace with the scientific school of thought is the way forward.

“There have been ample advancements in scientific techniques. Rather than dismissing these, isn’t it better if we utilize them?” asks Zafarul Islam Khan, the president of the All India Muslim Majlis-e-Mushawarat, an umbrella body for Muslim organizations.

For Mr. Mehta, his mood as well as his holiday has been affected by the moon.

“Whatever the order is now, we have to comply by it,” he said. He now plans to depart for Rajasthan on Friday. “Hopefully,” he added.

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